Horrible gas mileage

I have a 99 4.0 and just this week or so its been about 25-30 degrees outside and ive been getting about six miles to the gallon. Last week I was getting about 17. Do I have a problem or is that just what the cold weather does to these things I have new plugs and wires, im changing the fuel filter today....what else could it be???

I'd suggest you check or replace your coolant temperature sensor. If the coolant temp sensor is out of range, it may be telling the PCM that the engine is much colder than it really is and causing it to dump too much fuel into the engine.

If you go this route, be sure to get the correct one. There is a coolant temperature sensor for the PCM and a coolant temperature sender for the instrument cluster guage. They are mounted near each other and look very similar. The sensor has a Gray/Red wire and a Light Green/Red wire to it.

-Rod

So where exactly is that located on the block? I just recently had the whole intake manifold gasket recall done. It has been alot colder than usual this week but i guess it wont hurt to try. About how much does that sensor cost???

Assuming you have the 4.0L, non-SOHC, the coolant temperature sensor is mounted front of engine, left of throttle body.

-Rod

I do have a SOHC....... I think i know what your talking about now.... Just the little screw in temp sensor?

Yep, two wire sensor threaded into the intake. According to the service manual, on the SOHC you will need to remove the thermostat and housing to replace the coolant temp sensor.

-Rod

well i was thinking about doing a coolant flush and change the thermostat this weekend so I guess ill be right in there. thanks alot man, i hope this fixes it.